Silvery arrows appear from thin air and circle around the wizard, shooting out to strike his foes.

Unlike other spells, this cannot be cast whilst in hand-to-hand combat. The spell summons D6+2 arrows which the wizard can use to shoot against one enemy model. The arrows have a range of24". Use the wizard’s own Ballistic Skill to determine whether he hits or not, but ignore movement, range and cover penalties. The arrows cause one S3 hit each.

I have never heard your interpretation before, but I can see where you might think so. However there is no mention of a single rate of fire, just a single target. Our Warlocks shoot the arrows all at once.

The 'one shot per turn' thing is only for shooting weapons. Although magic is cast in the shooting phase and some spells (particularly Silver Arrows) follow some of the same rules for shooting, the two are quite separate.

I am partial to 'Lesser Magic' because it is pretty good effectiveness for not very much difficulty.